This K99/R00 Award will provide the training in health services research and clinical obstetric practice needed to develop the candidate into an independent interdisciplinary researcher focusing on reproductive health disparities. The rate of cesarean delivery has reached epidemic proportions in the U.S. Overweight and obese women are at increased risk of cesarean, as well as short-term and long-term morbidities subsequent to cesarean delivery. However, very little is known about how to optimally provide obstetric care to overweight/obese women, to maximize their chance of successfully achieving a vaginal delivery. Patient- and systems-level factors are important determinants of mode of delivery. There are racial/ethnic disparities in cesarean delivery, and the relative contribution of obesity and race i unknown. Additionally, very little is known about the effect of busy (high-volume) days in Labor & Delivery on cesarean delivery rates. This project aims to disentangle the effects of obesity and race/ethnicity, and establish the impact of daily obstetric volume, on cesarean delivery. The proposed K99/R00 study will use a large administrative dataset containing a diverse population of births (California) to tease out the impact of obesity and race/ethnicity on mode of delivery, exploring the possibility of effect modification. Interaction of this type has been observed for obesity and race effects on other obstetric outcomes. The K99 phase will allow the candidate to develop a metric of daily obstetric volume, or how busy a Labor & Delivery unit is on a given day. In the R00 phase, the candidate will analyze the impact of high-volume days on the nulliparous, term, singleton, vertex cesarean delivery rate. Analyses will also be conducted within the overweight/obese populations and among subgroups of racial minority women, to see if altered processes of obstetric care affect their outcomes differentially. These innovative analyses and methodologies will provide much-needed information on non-medical predictors of cesarean delivery among women at the greatest risk of adverse pregnancy outcomes. Oregon Health and Science University is the ideal setting to conduct this training and research, because of its leadership in clinical obstetrics, obstetric outcomes research, and health services research. The candidate will also leverage the resources at the Oregon Clinical and Translational Research Institute to foster professional development and facilitate the transition to research independence.